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<blockquote data-quote="Umbran" data-source="post: 7557713" data-attributes="member: 177">Haven't gone through the whole thread yet, but... The OP has mis-characterized what science considers an &quot;extinction level event&quot;.An ELE is *not* an event that causes the extinction of the human race.&nbsp; Or of any particular species.&nbsp; An ELE is an event which causes the extinction of most of the species of life on the planet, or otherwise vastly reduces biodiversity on the planet.&nbsp; It seems a little strange to me to say that an asteroid strike or major volcanic event are &quot;probably not&quot; ELE in the OP, when we can associate several historical extinction events to asteroid impacts and volcanic activity.Humans have this weird way of looking at risk.&nbsp; It is true that the vast majority of meteoric impacts on Earth are not really a big deal.&nbsp; But, is it also true that the impact of something a couple of kilometers across will cause an extinction event, pretty much guaranteed.&nbsp; Those impacts are rare, but their results are not negotiable.Of course, we seem to be within an ELE right now - and not due to climate change - the rate of species extinction has been at about 1000 times its normal background level since about the year 1900 (on geologic timescales, something that takes a couple of centuries is still an event).&nbsp; Human industrialization and expansion is driving extinctions far more quickly than it is driving speciations.&nbsp; We haven't yet reached the point of removing half the species on the planet, but if we don't change our behavior, it is only a matter of time.</blockquote>

[QUOTE="Umbran, post: 7557713, member: 177"] Haven't gone through the whole thread yet, but... The OP has mis-characterized what science considers an "extinction level event". An ELE is *not* an event that causes the extinction of the human race. Or of any particular species. An ELE is an event which causes the extinction of most of the species of life on the planet, or otherwise vastly reduces biodiversity on the planet. It seems a little strange to me to say that an asteroid strike or major volcanic event are "probably not" ELE in the OP, when we can associate several historical extinction events to asteroid impacts and volcanic activity. Humans have this weird way of looking at risk. It is true that the vast majority of meteoric impacts on Earth are not really a big deal. But, is it also true that the impact of something a couple of kilometers across will cause an extinction event, pretty much guaranteed. Those impacts are rare, but their results are not negotiable. Of course, we seem to be within an ELE right now - and not due to climate change - the rate of species extinction has been at about 1000 times its normal background level since about the year 1900 (on geologic timescales, something that takes a couple of centuries is still an event). Human industrialization and expansion is driving extinctions far more quickly than it is driving speciations. We haven't yet reached the point of removing half the species on the planet, but if we don't change our behavior, it is only a matter of time. [/QUOTE]

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